Hydraulic clutch control mechanism for a multi-mode hybrid transmission

Abstract

An electrically variable transmission (EVT) selectively establishes various EVT modes and a neutral mode. The EVT includes a source of pressurized fluid, fluid-actuated clutches, various solenoid-actuated valves including trim valves and blocking valves adapted to control a flow of pressurized fluid to the clutches to establish the transmission operating modes, and an electronic control unit (ECU). The ECU actuates different combinations of the solenoid-actuated valves to establish the different transmission modes. The solenoid-actuated valves are configured in such a manner as to provide the EVT with one or more default operating modes in the event the ECU temporarily loses electrical power. Depending on the particular configuration, the default modes can be the neutral mode alone, or the neutral mode combined with one or more of the EVT modes, with the EVT modes enabled by providing one or both of the blocking valves with a latching feature.

1. An electrically variable transmission (EVT) for a vehicle, the EVT being operable for selectively establishing a plurality of transmission operating modes including a neutral mode and a plurality of EVT modes providing progressively higher speed/lower torque conditions, the EVT comprising:
 a source of pressurized fluid; 
 a plurality of clutches each being selectively engagable using pressurized fluid from said source; 
 a plurality of solenoid-actuated valves each configured to control a flow of said pressurized fluid to at least one of said plurality of clutches, said plurality of solenoid-actuated valves including:
 a first, a second, a third, and a fourth trim valve each selectively controlling an admission of said pressurized fluid into at least one of said plurality of clutches; and 
 a first and a second blocking valve for selectively blocking an admission of said pressurized fluid into at least one of said first, second, third, and fourth trim valves, wherein one of said first and said second blocking valves is a latching device having a first and a second position; and 
 
 an electronic control unit (ECU) operable for selectively actuating different combinations of said plurality of solenoid-actuated valves to thereby establish the plurality of transmission modes based at least partially on a speed of the vehicle; 
 wherein said plurality of solenoid-actuated valves are configured to provide the EVT with multiple different default modes in the event of an electrical power failure at said ECU, said default modes including the neutral mode when said latching device is latched in the first position after said electrical power failure, and an EVT mode selected from the plurality of EVT modes that is established when the latching device is latched in the second position after said electrical power failure. 
 
     
     
       2. The EVT of  claim 1 , wherein said default modes further include a predetermined pair of EVT modes selected from the plurality of EVT modes; and
 wherein each of said first and said second blocking valves is configured as the latching device suitable for establishing said predetermined pair of EVT modes as a pair of said default modes. 
 
     
     
       3. The EVT of  claim 2 , wherein the plurality of EVT modes includes a first, a second, a third, and a fourth EVT mode each adapted for use at progressively higher speed/lower torque conditions;
 wherein said default modes include the neutral mode when neither of said latching devices are latched in the first position after said electrical power failure; 
 wherein one of said predetermined pair of EVT modes is said first EVT mode when one of said latching devices is latched in said first position and the other is latched in said second position after said electrical power failure; and 
 wherein another of said predetermined pair of EVT modes is said fourth EVT mode when each of said latching devices are latched in said second position after said electrical power failure. 
 
     
     
       4. A hydraulic control module (HCM) for an electrically-variable transmission (EVT) having a plurality of fluid-actuated clutches and a plurality of valves each selectively controlled by a corresponding electro-mechanical solenoid device, the plurality of valves including a first and a second blocking valve, the HCM comprising:
 a supply of pressurized fluid; 
 an electronic control unit (ECU) operable for selecting one of the different transmission modes based at least partially on a speed of the vehicle, said ECU being adapted to control the open and closed state of each of the plurality of valves by selectively actuating the corresponding electro-mechanical solenoid device, and wherein said open state allows an admission of said pressurized fluid into a corresponding one of the fluid-actuated clutches; 
 wherein the second blocking valve is configured as a latching device, and wherein the HCM:
 provides the EVT with multiple different default modes in the event of an electrical power failure at said ECU; 
 allows the EVT to default to a neutral mode as one of said default modes when said first blocking device is on and said second blocking device is latched during said electrical power failure; and 
 allows the EVT to default to a predetermined single EVT mode as another of said default modes when said first blocking device is on and said second blocking valve is not latched during said electrical power failure. 
 
 
     
     
       5. The HCM of  claim 4 , wherein the plurality of fluid-actuated clutches includes a first, second, third, and fourth clutch each controlled by a dedicated trim valve;
 wherein the
 first blocking valve is configured to selectively block a flow of said pressurized fluid to said first clutch; and 
 said second blocking valve is configured to selectively block a flow of said pressurized fluid to the second and third clutch, wherein said first and said second blocking valves are configured as latching devices; and 
 
 wherein the HCM allows the EVT to default to: said neutral mode when said second blocking valve is latched during said electrical power failure; a first EVT mode when said first blocking valve is latched and said second blocking valve is not latched during said electrical power failure; and a second EVT mode when neither of said first and said second blocking valves are latched during said electrical power failure. 
 
     
     
       6. The HCM of  claim 5 , wherein the EVT is configured to provide four different EVT modes each providing progressively higher speed/lower torque operation, and wherein said first EVT mode provides the lowest speed/highest torque operation of said four different EVT modes.